1. Field of the Invention
The invention relates generally to explosive tools and more particularly to a means of remotely initiating an M81 shock tube igniter.
2. Background
An M81 igniter is used to ignite a time blasting fuse or to initiate a shock tube. Shock tube is a thin plastic tube with a thin layer of special explosive material deposited on its interior surface. The standard M81 igniter has the following visible components: a small plastic tube with a pull-ring on a pull-rod projecting from one end, a safety (cotter) pin that passes through the tube, and a screw cap that secures a holding mechanism for the fuse or shock tube. The igniter can accommodate a shock tube or a time blasting fuse. A two-piece plastic plug allows proper securing of the shock tube (with just inner piece removed) or the time blasting fuse (with both pieces removed). A partially cut away prior art view of an M81 is shown in FIG. 6.
The M81 was engineered to be manually actuated by the operator. The ignition sequence is typically as follows: An operator (explosive expert) while positioning an explosive charge at the desired distance from the target, begins dispenses shock tube/time blasting fuse from the dispenser. After the explosive charge has been positioned, the operator moves away, continuing to dispense the shock tube/time blasting fuse until a sufficient pay-out length has been deployed to reach a safe area for personnel. The shock tube is then connected to the igniter. To make this connection the operator loosens the screw cap and removes some or all of the inner piece of the two-piece plastic plug, cuts off an end of the tube/fuse and inserts it in the hole from which the plug was removed. The screw cap is then re-tightened to secure the fuse or shock tube. The safety (cotter) pin can then be removed. To initiate the M81, while holding the body of the M81, the operator uses his other hand to pull on the pull-ring, which in turn pulls out the pull-rod. The pull-rod pulls the firing-pin against the force of a spring. When the limit of travel is reached, the pull-rod releases the firing-pin, which is forced by the spring into the primer, which fires with a flame and an explosive shock which ignites the fuse or initiates the shock tube, therein detonating the explosive charge.
In more recent developments, the shock tube can be manually initiated using an electrical spark produced by a sparking device attached to a robotic device. In both cases (M81 and sparking device) manual ignition is required. An example of the robotic device is the MTRS platform (Man Transportable Robotic System). Initiating shock tube by hand requires the robot operator to maneuver the robot from the target site, dispense a sufficient pay-out length until enough has been deployed for the operator to move away, while continuing the dispensing shock tube, to a safe area. This method of operation is time consuming and prevents additional investigation once the shock tube deployment begins. Another method of initiating shock tube is by an electrical spark produced by a firing device attached to the MTRS robotic platform. This method requires tethering the robot to the shock tube. The tethering prevents free movement of the robot, and is problematic. For instance, if a robot runs over the shock tube, the shock tube can become tangled in the drive tracks of the robot, limiting the robot's movement.